The present invention relates generally to surgical devices for implanting substances within the body of a patient for therapeutic purposes. More specifically the present invention relates to a needle for implanting radioactive seeds within the body of a patient for localized radiation treatment of a tumor.
It is well known to treat tumors with localized radiation by implanting radioactive seeds within the body of the patient within or in the vicinity of the tumor. The seeds typically comprise I-125, Pd-103, or other suitable radioactive agent contained within a pellet or seed to prevent migration of the radioactive material throughout the body of the patient.
Such radioactive seeds, known as xe2x80x9cbrachytherapyxe2x80x9d seeds, are conventionally implanted within the body of the patient by advancing the seeds through a hollow needle or xe2x80x9cstyletxe2x80x9d with a push rod or cannula. Since it is usually desirable to implant a number of seeds in a single procedure, a plurality of seeds can be loaded into the stylet. To assure proper spacing between adjacent seeds, spacers of cat gut or other bioabsorbable material may be placed between adjacent seeds. The needle is then inserted into the body of the patient to a location adjacent the tumor. The physician then holds the cannula steady as the stylet is withdrawn, pushing the seeds and spacers out into the tissues of the patient as the stylet is retracted.
Conventional brachytherapy seed needles suffer a number of disadvantages. Because the seeds are housed within the forward end of a steel needle when inserted into the tissues of the patient, it is not possible to visualize the exact position of the seeds using ultrasound or other medical imaging technology. Accordingly there is a need for a needle for implanting brachytherapy seeds which permits the location of the seeds to be visualized by medical imaging technology prior to the seeds being deployed.
Another problem concerns a means for retaining the seeds in the forward end of the needle. To prevent the seeds from falling out of the needle, the forward end of the needle must be closed, such as with a plug of a biodegradable material. Thus, when the brachytherapy seeds are pushed out into the patient, the plug is also pushed out into the patient and remains in the patient. It would thus be desirable if there were a brachytherapy needle which did not require to prevent the seeds from falling out a plug which would be implanted into the patient""s body along with the seeds.
The number and location of brachytherapy seeds used in a given treatment is carefully calculated to deliver a predetermined dose of radiation to the tumor. Since the amount of radiation delivered to a tumor depends upon the spacing and location of the seeds relative to the tumor, optimal brachytherapy treatment requires careful positioning of the seeds. A problem associated with prior art brachytherapy procedures is that friction between the brachytherapy needle and the tissues of the patient can cause the seeds to be improperly positioned. More specifically, as the cannula of the brachytherapy needle is retracted to expose the seeds in the tissues of the patient, friction between the outer surface of the cannula and the patient""s tissues causes the tissues to distend. The seeds are deployed into the distended tissue. When the frictional force is removed, the tissue subsequently returns to its normal position, causing the seeds to be displaced as the tissue moves. The seeds may thus not be positioned in the desired locations. Thus there is a need for a way to reduce or eliminate the effect of friction between the brachytherapy needle and the surrounding tissue as the seeds are being implanted.
Finally, after the procedure is finished, the brachytherapy needle itself becomes a biohazard. The sharp tip of the cannula lends itself to accidental needle sticks. Thus there is a further need for a brachytherapy seed needle which minimizes the possibility of accidental needle sticks.
Stated generally, the present invention comprises an improved needle for implanting radioactive seeds which addresses each of the disadvantages associated with conventional brachytherapy needles. The brachytherapy needle of the present invention permits the radioactive seeds to be visualized using medical imaging technology prior to the seeds being discharged from the needle. Thus the needle can be repositioned if necessary for accurate placement of the seeds. In a disclosed embodiment the needle also retains the seeds within the needle without the need for a plug which will be left within the patient""s body. In one aspect of the invention the needle substantially eliminates the possibility of the brachytherapy seeds being improperly placed as a result of friction between the needle and the surrounding tissue distending the tissue as the needle is withdrawn. And the design of the needle of the disclosed embodiment is such that, after normal use, the cutting forward edge of the needle is shielded without any active intervention on the part of the physician to prevent accidental needle sticks.
Stated somewhat more specifically, the present invention relates to a brachytherapy needle in which radioactive seeds are delivered into the body of a patient by pushing them with a stylet through a hollow tube. In a first aspect the needle assembly of the present invention comprises a transparent or translucent tube into which the radioactive seeds and intervening spacers are loaded, such that the seeds and spacers can be seen within the tube. The physicist who loads the seeds, the radiation oncologist, and the urologist thus all have the option of visually inspecting the tube to insure that the seeds are properly loaded.
In another aspect the needle assembly of the present invention comprises a tube into which the seeds are loaded and which is telescopically disposed within a cutting cannula. The tube is substantially longer than the cannula such that the cannula can be withdrawn over the tube, leaving the forward end of the tube exposed within the tissues of the patient. The tube is formed from a material which is transparent to the medical imaging modality being used. When the cannula is retracted, the seeds within the tube can be visualized within the tissues of the patient using conventional medical imaging technology.
In another aspect the needle of the present invention includes a deformable constriction which retains the seeds within the lumen of the needle against the force of gravity but which deforms to permit the seeds to pass when subjected to a force greater than the force of gravity.
In still another aspect the needle of the present invention has a low-friction exterior surface to prevent tissue from being displaced as the needle is withdrawn. In one disclosed embodiment the tube has a low-friction coating applied to its exterior surface. Coating material is permitted to accumulate within the forward end of the tube, thereby forming a deformable constriction which retains the seeds within the lumen of the needle against the force of gravity but which deforms to permit the seeds to pass when subjected to a force greater than the force of gravity.
Another aspect of the invention relates to a conventional two-piece cannula and stylet brachytherapy needle design. The novel feature is a low-friction coating applied to the exterior surface of the cannula. Coating material is permitted to accumulate within the forward end of the cannula, thereby forming a deformable constriction which retains the seeds within the lumen of the cannula against the force of gravity but which deforms to permit the seeds to pass when subjected to a force greater than the force of gravity.
In yet another aspect the needle of the present invention comprises a cannula and a hollow tube in telescoping relation, the cannula and tube being dimensioned such that when the cannula is withdrawn with respect to the tube, the blunt forward edge of the tube extends beyond the cutting edge of the hollow cannula to prevent accidental needle sticks.